Now that people's lifestyles and activities have been diversified, advertisement video images presented by the mass media and the like have significant influence on these various people. Moreover, because people crave for updated information due to the widespread use of the Internet, advertisement video images posted or displayed on a train are greatly expected to produce advertisement effects. It is considered that, especially because the space in the train is closed and restricts passengers' activities, the advertisement effects are remarkably large, and therefore the demand has been rapidly increasing. To satisfy this demand, an LCD arranged above a door of a train car has been used as a display medium to provide the service of carrying advertisement video such as moving images and still images, as well as operation information such as the destination, stations to make a stop, the currently traveling location, and delay information.
The advertisement video placed by an advertiser contains both sound-accompanying moving or still images and no-sound moving or still images. Because the sound that accompanies the advertisement video may interrupt announcement of the operation information and the destination information, or because passengers may confuse switching of a sound-accompanying advertisement to a no-sound advertisement with a breakdown of the announcement system, they tend to be presented without sound or with caption. On the other hand, to make the advertisement video designed for a TV commercial or the like more appealing to passengers, there is a need for presenting it with accompanying sound.
As a means for satisfying such need, the advertising system described in Patent Document 1 below uses radio waves output from a wireless distributing device arranged on a train car to distribute sound to passengers' portable radios or the like.    [Patent Document 1] Japanese Patent Application Laid-open No. 2006-259253